A few days ago, Wired News carried a story by Sean Captain about the Healthmap project, a mash-up of Google Maps and various disease reporting services:

The new Healthmap website digestsinformation from a variety of sources ranging from the World Health
Organization to Google News and plots the spread of about 50 diseases
on a continually updated global map. It was developed as a side project
by two staffers at the Children's Hospital Informatics Program in Boston -- physician John Brownstein and software developer Clark Freifeld.

The Wired News story starts out with this lead: "Web-based maps are handy for keeping tabs on weather and traffic, so why not for disease outbreaks, too?" And the title is "Get Your Daily Plague Forecast," which. because it is a tad trite, I find rather ironic because a recent PNAS paper demonstrates that, "Plague dynamics are driven by climate variation."

Stenseth, et al., studied the prevalence of Yersinia pestis in the primary host animal, gerbils, as a function of average temperature over 45 years in Central Asia. They find that ,"A 1°C increase in spring is predicted to lead to a >50% increase in prevalence." The virus causes bubonic plague in humans, and transmission from rodents to humans is thought to be the main route into the human population. The authors note in the abstract that:

Climatic conditions favoring plague apparently existed in this region at the onset of the Black Death as well as when the most recent plague pandemic arose in the same region, and they are expected to continue or become more favorable as a result of climate change. Threats of outbreaks may thus be increasing where humans live in close contact with rodents and fleas (or other wildlife) harboring endemic plague.

And as a cheery final note, they conclude that:

Our analyses are in agreement with the hypothesis that the Medieval Black Death and the mid-19th-century plague pandemic might have been triggered by favorable climatic conditions in Central Asia. Such climatic conditions have recently become more common and whereas regional scenarios suggest a decrease in annual precipitation but with increasing variance, mean spring temperatures are predicted to continue increasing. Indeed, during the period from the 1940s, plague prevalence has been high in its host-reservoir in Kazakhstan. Effective surveillance and control during the Soviet period resulted in few human cases. But recent changes in the public health systems, linked to a period of political transition in Central Asia, combined with increased plague prevalence in its natural reservoir in the region, forewarn a future of increased risk of human infections.

The combination of climate influences on the prevalence of infectious disease, documented climate change over the last few decades, and the rise of megacities is something we definitely need to watch.